fn main(){
    let s = getline();
    let s = s.trim();
    let v:Vec<&str> = s.split(" ").collect();
    let a = v[0].parse::<i32>().unwrap();
    let b = v[1].parse::<i32>().unwrap();
    let mut count :i32 = 0;
    for i in a..(b+1){
        if (a + i + b)%3 == 0 {
            count+=1;
        }
    }
    println!("{}", count);
}
fn getline() -> String{
	let mut __ret=String::new();
	std::io::stdin().read_line(&mut __ret).ok();
	return __ret;
}